706 REPORT— 1894. 



Again, tlie few temperatures that have been ohtained in the eastern South 

 Pacific show a considerable difference from those in the South Atlantic, and we 

 are compelled to assume a ridge from the Falkland Islands to the Antarctic 

 continent. 



It is interesting that the investigation into the translation of the great seismic 

 wave caused by the eruption of Krakatoa in 1883 led to a similar and entirely 

 independent conclusion. The wave caused by the explosion in the Straits of Sunda 

 reached Cape Horn, where by good chance a French meteorological expedition had 

 erected an automatic tide gauge, but instead of one series of waves being marked 

 on the paper there were two. A little consideration showed that the South Pole 

 having directly interposed between Sunda Straits and Cape Horn, the waves 

 diverted by the land about the pole would arrive from both sides. 



One wave, however, made its appearance seven hours before the other. 



Study showed that the earliest wave comcidsd in time with a wave travelling 

 on the Pacific side of the pole, with a velocity due to the known depth, while the 

 later wave must have been retarded in its journey via the South Atlantic. The 

 only possible explanation is that the wave had been impeded by comparatively 

 shallow water. 



The evidence from bottom temperature was then unknown, and thus does one 

 branch of investigation aid another. 



In the Western Pacific the water is colder, a few bottom temperatures of a 

 little over 33° F. having been found in the deep trough east of the Tonga Islands; 

 but the North Pacific, though the deeper ocean — of enormous area and volume — 

 is apparently again cut off by a submarine ridge. The north-western part of the 

 Indian Ocean is for similar reasons assumed to be divided from the main body, the 

 shallower water probably running from the Seychelles to the Maldive Islands. 



Mr. Buchanan has pointed out why some parts of oceans, deep and vast though 

 they be, are when cut off from communication with others warmer at the bottom. 



Water can only sink through lower layers when it is the heavier, and though 

 a warm surface cun-ent becomes from evaporation denser, its heat makes it specifi- 

 cally lighter than the strata below. 



It is only when such a current parts gradually with its heat, as in travelling 

 from tropical to temperate regions, that it sinks and slowly but surely carries 

 its temperature with it, modifying the extreme natural cold of the bottom layers. 



In the North Atlantic and Pacific we have such a condition. The great 

 currents of the Gulf Stream and Japan current as they flow to the north sink, and 

 in the course of ages have succeeded in raising the bottom temperature three or 

 four degrees. 



In the Southern Seas this influence is not at work, and, directly connected with 

 the more open water round the South Pole, there is nothingto carry to the abysmal 

 deptbs any heat to raise them from their normal low temperatures, due to the 

 absence of any heating influence. 



The ice masses round the South Pole have probably little or no effect on bottom 

 temperature, as the fresher, though colder, water will not sink ; and, as a matter 

 of fact, warmer water is found at a few hundred fathoms than at the surface. 



The lowest temperature ever obtained was by Sir John Ross in the Arctic 

 Ocean in Davis Straits at a depth of 680 fathoms, when he recorded a reading of 

 25° F. This probably requires confirmation, as thermometers of those days were 

 somewhat imperfect. 



In the great oceans the greatest cold is found on the western side of the South 

 Atlantic, where the thermometer stands at 32°-3 F., but temperatures of 29° F. have 

 been obtained of recent years east of the Fseroe Islands, north of the ridge which 

 cuts off the deeper waters of the Arctic from the Atlantic. 



Though scarcely within the limits of my subject, which is the sea itself, I must 

 say a few words on the sea floor. 



The researches carried on in the ' Challenger ' revealed that while for a certain 

 distance from the continents the bottom is composed of terrestrial detritus, every- 

 where in deep water it is mainly composed of the skeletons or remains of skeletons 

 of the minute animals that have lived in the water. 



